Die-cast component, body component having said die-cast component, motor vehicle having said body component, and method for producing said die-cast component

ABSTRACT

A method for producing a die-cast component and a die-cast component that is produced therewith. According to the invention, an outstanding punch riveting suitability is achieved if the die-cast component has a temperable aluminum alloy with the following alloying components: from 5.0 to 9.0 wt % silicon (Si), from 0.25 to 0.5 wt % magnesium (Mg), and residual aluminum as well as inevitable production-related impurities, containing at most 0.05 wt % of each and at most 0.15 wt % collectively, wherein the die-cast component has a yield strength (Rp0.2) of greater than 190 MPa and an elongation at break (A5) of greater than or equal to 7% and the uniform elongation (Ag) and necking elongation (Az) satisfy the condition Az≥Ag/2.

TECHNICAL FIELD

The invention relates to a die-cast component and a method for producing said die-cast component.

PRIOR ART

In a thin-walled die-cast component such as structural components for motor vehicles, in order to bring the strength (R_(p0.2), R_(m)) and the ductility (or elongation at break A₅) into a desired relationship to each other—so that for example, it is possible to comply with crash-relevant SDI values [SDI=strength-ductility index, which is calculated from the material properties R_(m), R_(p0.2), and A₅, namely SDI=(R_(m)+3*R_(p0.2))/4*A₅/100] in the automotive sector—, EP3176275A1 proposes a heat treatment of an Al—Si aluminum alloy with a two-stage annealing, quenching, and three-stage artificial aging. This method also leads to a good punch riveting suitability—i.e. a joining by means of shaping—, which essentially depends on the ductility of the die-cast component. Punch riveting using a domed die plate as compared to other die plates (flat die plate, spherical die plate, etc.) particularly requires the maximum deformability in the die-cast component. If the deformability of the material is not sufficient, then cracks form on the die plate side of the die-cast component. Another improvement of the punch riveting suitability by increasing the ductility, on the other hand, necessitates losses in he strength — which disadvantageously reduces crash-relevant SDI values.

DISCLOSURE OF THE INVENTION

Based on the prior art explained at the beginning, the object of the invention is to create a die-cast component, which in comparison to known die-cast components, features an improved punch riveting suitability with the same elongation at break and strength.

The invention attains the stated object by means of the features of claim 1.

By virtue of the die-cast component having a temperable aluminum alloy with 5.0 to 9.0 wt % silicon (Si) and from 0.25 to 0.5 wt % magnesium (Mg) and residual aluminum as well as inevitable production-related impurities containing at most 0.05 wt % of each and at most 0.15 wt % collectively, it is possible to enable a comparatively high yield strength (R_(p0.2)) of greater than 190 MPa and also an elongation at break A₅ of greater than or equal to 7%.

-   Si: 5.0 to 9.0 wt % silicon (Si), which represents a reduced     percentage in comparison to the prior art, can significantly reduce     the percentage of crack-inducing primary phases (namely eutectic     silicon particles). This reduces its negative influence in the     joining by means of shaping. -   Mg: 0.25 to 0.5 wt % magnesium (Mg) can enable a yield strength     (R_(p0.2)) of greater than 190 MPa.

In particular, though, the punch riveting suitability of the die-cast component improves because the uniform elongation (A_(g)) and necking elongation (A_(z)) satisfy the condition A_(z)≥A_(g)/2. As a result, this high-strength die-cast component, even in a thin-walled embodiment, can undergo joining by means of shaping, for example punch riveting or clinching, without cracking.

In addition to Si and Mg, the aluminum alloy can optionally have one or more alloying elements from the following group: up to 0.8 wt % manganese (Mn), from 0.08 to 0.35 wt % zinc (Zn), from 0.08 to 0.35 wt % chromium (Cr), up to 0.30 wt % zirconium (Zr), up to 0.25 wt % iron (Fe), up to 0.15 wt % titanium (Ti), up to 0.20 wt % copper (Cu), up to 0.025 wt % strontium (Sr), up to 0.2 wt % vanadium (V), and/or up to 0.2 wt % molybdenum (Mo).

The above-mentioned punch riveting suitability can be further improved if the die-cast component has a uniform elongation (A_(g)) of at least 6% and a necking elongation (A_(z)) of at least 4%.

In addition, in the aluminum alloy according to the invention, the following content or contents are conceivable for silicon (Si) and/or zinc (Zn) and/or magnesium (Mg) and/or manganese (Mn) and/or copper (Cu) and/or iron (Fe) and/or titanium (Ti) and/or strontium (Sr):

-   -   from greater than 6.5 to 9.0 wt % silicon (Si),     -   more particularly from greater than 6.5 to 8 wt % silicon (Si)     -   from 0.3 to 0.5 wt % magnesium (Mg)     -   from 0.3 to 0.6 wt % manganese (Mn)     -   from 0.15 to 0.3 wt % zinc (Zn),     -   more particularly from 0.15 to 0.25 wt % zinc (Zn)     -   from 0.10 to 0.20 wt % copper (Cu)     -   from 0.10 to 0.25 wt % iron (Fe),     -   more particularly from 0.15 to 0.25 wt % iron (Fe)     -   from 0.05 to 0.15 wt % titanium (Ti)     -   from 0.015 to 0.025 wt % strontium (Sr)

Particularly high SDI values can be achieved if the temperable aluminum alloy has from greater than 6.5 to 9.0 wt % silicon (Si), more particularly from greater than 6.5 to 8 wt % silicon (Si).

-   Si: For example 6.5<wt % silicon (Si)≤9.0, while achieving     sufficiently good castability of the alloy, can also reduce     crack-inducing primary phases, which can improve the joining by     means of shaping even further—this is even more the case if the     condition 6.5<wt % silicon (Si)≤8.0 is satisfied.

Strength and ductility can be improved further if the aluminum alloy has from 0.15 to 0.3 wt % zinc (Zn) and/or from 0.3 to 0.5 wt % magnesium (Mg).

-   Zn: A zinc (Zn) content of from 0.15 to 0.3 wt % can further improve     the ductility of the die-cast component. Preferably, there is a zinc     (Zn) content of from 0.15 to 0.25 wt %. -   Mg: A magnesium (Mg) content of from 0.3 to 0.5 wt % can further     increase the yield strength (R_(p0.2)).

The castability of the die-casting alloy can be further improved if the aluminum alloy has from 0.3 to 0.6 wt % manganese (Mn).

The strength of the aluminum alloy can be increased further with a copper (Cu) content of from 0.10 to 0.20 wt %.

In addition, by means of this copper content, the aluminum alloy can have a higher secondary aluminum content, which can be increased further if the aluminum alloy 0.15 to 0.25 wt % iron (Fe). This is more particularly the case if the aluminum alloy has from 0.15 to 0.25 wt % iron (Fe).

The ductility and strength of the aluminum alloy can be improved with 0.05 to 0.15 wt % titanium (Ti); the ductility can be optimized further with from 0.015 to 0.025 wt % strontium (Sr).

It is also conceivable for the aluminum alloy to have up to 0.05 wt % manganese (Mn) and/or up to 0.05 wt % copper (Cu).

-   Mn: A manganese (Mn) content of up to 0.05 wt % can lead to a     significant increase in ductility. Such a limitation of the     manganese content can specifically reduce the percentage of     crack-inducing primary phases (manganese-containing intermetallic     phases) even further, which would structurally weaken the die-cast     component, more particularly during the joining by means of shaping. -   Cu: A copper (Cu) content of up to 0.05 wt % can also reduce the     cracking tendency, which can further simplify the joining by means     of shaping and can further improve the punch riveting.

The die-cast component according to the invention is more particularly suitable for use as a body component for a motor vehicle. Preferably, the die-cast component is firmly connected to the other component by means of a punch rivet. The die-cast component is preferably used as a body component of a motor vehicle.

Based on the prior art explained at the beginning, another object of the invention is to modify the method in order to further improve the punch riveting suitability while preserving almost the same SDI values in the die-cast component. It should also be possible to embody the method in a simple-to-implement and reproducible way.

The invention attains the stated object with regard to the method by means of the features of claim 9.

If a temperable aluminum alloy with 5.0 to 9.0 wt % silicon (Si) and from 0.25 to 0.5 wt % magnesium (Mg) and residual aluminum as well as inevitable production-related impurities containing at most 0.05 wt % of each and at most 0.15 wt % collectively, then it is possible to perform a special heat treatment.

-   Si: With 5.0 to 9.0 wt % silicon (Si), it is first of all possible,     due to the lower limit of 5.0 wt %, to insure the castability of the     aluminum alloy even with complex contours. It is also possible, due     to the upper limit of 9.0 wt % silicon (Si), to prepare the aluminum     alloy for an annealing treatment at higher temperatures. -   Mg: With 0.25 to 0.5 wt % magnesium (Mg), the aluminum alloy can be     prepared for the achievement of an increased strength, more     particularly the yield strength (R_(p0.2)).

Based on these Si and Mg contents, the Al-Si alloy is thus prepared for an increased strength with a reduced ductility—namely in that a first annealing is performed at a temperature in the range from 320° C. (degrees Celsius) to 450° C. for a duration of from 20 to 75 minutes and a second annealing at a temperature in the range from 510° C. to 540° C. for a duration of from 5 to 35 minutes, i.e. at elevated temperatures compared to the prior art. By means of the quenching that follows the annealing and takes place with a temperature gradient in the range of greater than 4 K/s, the properties (increased strength with reduced ductility) are adjusted in the die-cast component.

A shifting of the mechanical properties from ductility in the direction of strength can subsequently be compensated for through an overaging of the die-cast component with the aid of an at least three-stage artificial aging.

For this purpose, it has turned out to be advantageous if a first artificial aging takes place at a temperature in the range from 100° C. to 180° C. for a duration of from 40 minutes to 150 minutes, a second artificial aging takes place at a temperature in the range from 180° C. to 300° C. for a duration of from 30 minutes to 100 minutes, and a third artificial aging takes place at a temperature in the range from 230° C. to 300° C. for a duration of from 5 minutes to 120 minutes. It is thus possible to achieve a T7 state in the die-cast component, which not only satisfies predetermined SDI values composed of strength (R_(p0.2), Rm) and ductility or elongation at break A₅, but surprisingly also has a significant increase in the punch riveting suitability.

Tests have shown that the method according to the invention exerts particular influence on the ratio between the necking elongation (A_(z)) and uniform elongation (A_(g)), which necking elongation A_(z) is determined by the equation A_(z)=A(bzw. A₅)-A_(g). According to the invention, with a comparatively high-strength Al—Si aluminum alloy in the T7 state, a necking elongation A_(z) is thus produced, which is greater than or equal to A_(g)/2—which insures a crack-free punch riveting, more particularly also a punch riveting using a domed die plate, which requires a particularly high deformability of the die-cast component on the die plate side.

This can be achieved even with a thin-walled die-cast component, for example for vehicle body construction, which cannot currently be reliably used for a joining by means of shaping, primarily a punch riveting.

In addition, in comparison to known other methods, the method according to the invention requires only an adaptation in temperature and holding time—which is comparatively simple to implement and thus improves the reproducibility of the method.

The method according to the invention can therefore insure the production of a die-cast component, which has a yield strength (R_(p0.2)) of greater than 190 MPa and an elongation at break (A₅) of greater than or equal to 7% and whose uniform elongation (A_(g)) and necking elongation (A_(z)) satisfy the condition A_(z)≥A_(g)/2.

Preferably, the produced die-cast component can have a uniform elongation (A_(g)) of at least 6% and a necking elongation (A_(z)) of at least 4%.

In addition to Si and Mg, the aluminum alloy can optionally have the following additional alloying elements, namely up to 0.8 wt % manganese (Mn), from 0.08 to 0.35 wt % zinc (Zn), from 0.08 to 0.35 wt % chromium (Cr), up to 0.30 wt % zirconium (Zr), up to 0.25 wt % iron (Fe), up to 0.15 wt % titanium (Ti), up to 0.20 wt % copper (Cu), up to 0.025 wt % strontium (Sr), up to 0.2 wt % vanadium (V), and/or up to 0.2 wt % molybdenum (Mo).

The necking elongation A_(z) can be improved further if the first annealing takes place at a temperature in the range from 390° C. to 410° C. and/or for a duration of from 50 minutes to 70 minutes. In addition, by means of this comparatively narrow temperature and time range, it is possible to more reproducibly exert an influence on the mechanical properties of the finished die-cast component.

If the second annealing takes place at a temperature in the range from 520° C. to 535° C., more particularly from 525° C. to 535° C., and/or for a duration of from 25 to 30 minutes, then it is possible to avoid a distortion of the die-cast component, for example due to the comparatively short holding time. In addition, this also improves the reproducibility of the method.

The strength values can be adjusted within comparatively narrow limits if the quenching takes place with a temperature gradient in the range from 7 K/s to 20 K/s.

This accelerated cooling can take place, for example, through cooling in moving air, etc.

Preferably, the first artificial aging takes place at a temperature in the range from 140° C. to 160° C. and/or for a duration of from 110 minutes to 130 minutes in order to initially bring the die-cast component into a T64 state.

A T6 state in the die-cast component is achieved in that the second artificial aging takes place at a temperature in the range from 190° C. to 210° C. and/or for a duration of from 50 minutes to 70 minutes.

If the third artificial aging takes place at a temperature in the range from 230° C. to 270° C. and/or for a duration of from 10 minutes to 30 minutes, then it is possible to adjust the strength and ductility of the die-cast component even more precisely. More particularly, however, this makes it possible to achieve a comparatively high necking elongation (A_(z)), which can reduce even further the risk of cracking during the punch riveting of the die-cast component.

BRIEF DESCRIPTION OF THE DRAWINGS

To prove the achieved effects, thin-walled die-cast components were produced from different casting alloys in the die-casting process. The subject matter of the invention is depicted by way of example in the figures. In the drawings

FIG. 1 shows a view of the sequence of the heat treatment according to the invention,

FIG. 2 a is a cutaway polished cross-section of two punch-riveted components, with the lower component being a die-cast component according to the prior art,

FIG. 2 b shows a three-dimensional view of FIG. 2 a from the die plate side,

FIG. 3 a is a cutaway polished cross-section of two punch-riveted components, with the lower component being the die-cast component according to the invention, and

FIG. 3 b shows a three-dimensional view of FIG. 3 a from the die plate side.

WAYS TO IMPLEMENT THE INVENTION

The compositions of the tested alloys are listed in Table 1; the alloying elements listed in this table are accompanied by residual aluminum as well as inevitable production-related impurities, containing at most 0.05 wt % of each and at most 0.15 wt % collectively.

TABLE 1 Overview of the aluminum alloys Si Mg Mn Fe Zn Zr Ti Sr Alloys wt % wt % wt % wt % wt % wt % wt % wt % AlSi10Mg0.4Mn 10.5 0.4 0.61 <0.22 0.2 0.15 0.06 0.02 AlSi7Mg0.4 7 0.4 0.05 <0.15 0.2 0.15 0.06 0.02

The alloy AlSi7Mg0.4 ranges within the content limits according to the independent claims. The alloy AlSi10Mg0.4Mn, in comparison to the alloy AlSi7Mg0.4, has a significantly higher Si content—and in this connection, therefore lies outside the content limits according to the invention.

The die-cast components P1 (prior art) and I1 (according to the invention) with the relevant Al—Si aluminum alloys were subjected to a subsequent heat treatment according to Table 2:

TABLE 2 Overview of the heat treatment Com- Annealing Artificial aging ponent Alloy First Second Quenching First Second Third P1 AlSi10Mg0.4Mn 400° C. 510° C. 3 K/s 120° C. 230° C.  1 h  30 min  2 h  1 h I1 AlSi7Mg0.4 400° C. 530° C. 7 K/s 150° C. 200° C. 250° C.  1 h  30 min  2 h  1 h  20 min

FIG. 1 shows the sequence of the heat treatment according to the invention in greater detail: First, a two-stage annealing takes place, namely a first annealing 1.1 and subsequent second annealing 1.2, after which a quenching 2 takes place and, after a certain storage time, a three-stage artificial aging takes place with a first heating 3.1, a subsequent second heating 3.2, and a subsequent third heating 3.3. In this heat treatment, the die-cast component I1 passes through various states from T4, T6 x, T6, up to T7, as indicated in FIG. 1 .

FIG. 1 also shows the difference in the second annealing 1.2 between the invention I1 and the prior art P1. The second annealing in the prior art P1 takes place at a distinctly lower temperature than in the invention I1.

By contrast with the invention, the die-cast component P1 lacks a third artificial aging. There are also significant differences in the parameters of the second annealing—these differences by and large lead to the fact that after the heat treatment, the die-cast component P1 is in the T6 state.

At the end, the two die-cast components P1 and I1 were tested to ascertain their mechanical properties. For this purpose the yield strength R_(p0.2), ultimate tensile strength R_(m), elongation at break A₅, and uniform elongation A_(g) were ascertained. The measurement results obtained are compiled in Table 3. The necking elongation A_(z) was calculated based on the elongation at break A₅ and the uniform elongation A_(g).

TABLE 3 Mechanical properties Component R_(p0.2) [MPa] R_(m) [MPa] A₅ [%] A_(g) [%] A_(z) [%] = A₅ − A_(g) P1 195 277 12.8 8.7 3.7 I1 195 250 12.4 6.7 6.1

According to Table 3, the die-cast component according to the invention I1 has a distinctly higher necking elongation (A_(z))—as a result of which the die-cast component I1 has a particularly good punch riveting suitability and is generally suitable for a joining by means of shaping.

This suitability was tested by means of a punch riveting using a domed die plate—specifically, an aluminum sheet A of the 6xxx series was punch riveted to the die-cast component P1 on the die sheet side and to the die-cast component I1 on the die sheet side using a rivet element N. The results of this punch riveting are shown in FIGS. 2 a & 2 b and 3 a & 3 b, respectively.

In the polished cross-section of AlSi10Mg0.4Mn in the T6 state shown in FIG. 2 a, several cracks R are visible, whereas in the polished cross-section of the Al—Si7Mg0.4 alloy according to the invention in the high-strength T7 state shown in FIG. 3 a, no cracks are visible.

In addition, the AlSi10Mg0.4 Mn T6 shown in FIG. 2 b exhibits numerous deep cracks on the die plate side whereas the cracks in the Al—Si7Mg0.4 T7 are much finer. There is in fact a larger number of them, but these are not critical because of their small width and depth. According to the invention, a riveting result is thus improved significantly compared to the prior art.

For this reason, the die-cast component according to the invention I1 also has a particularly good suitability, for example, for thin-walled shaped parts on a body of a vehicle, preferably a motor vehicle. 

1. A die-cast component made of a temperable aluminum alloy comprising the following alloy components: from 5.0 to 9.0 wt % silicon (Si), from 0.25 to 0.5 wt % magnesium (Mg), and optionally up to 0.8 wt % manganese (Mn), from 0.08 to 0.35 wt % zinc (Zn), from 0.08 to 0.35 wt % chromium (Cr), up to 0.30 wt % zirconium (Zr), up to 0.25 wt % iron (Fe), up to 0.15 wt % titanium (Ti), up to 0.20 wt % copper (Cu), up to 0.025 wt % strontium (Sr), up to 0.2 wt % vanadium (V), up to 0.2 wt % molybdenum (Mo) and residual aluminum as well as inevitable production-related impurities, containing at most 0.05 wt % of each and at most 0.15 wt % collectively, wherein the die-cast component has a yield strength (R_(p0.2)) of greater than 190 MPa and an elongation at break (A₅) of greater than or equal to 7% and a uniform elongation (A_(g)) and necking elongation (A_(z)) satisfy the condition A_(z)≥A_(g)/2.
 2. The die-cast component according to claim 1, wherein the die-cast component has a uniform elongation (A_(g)) of at least 6% and a necking elongation (A_(z)) of at least 4%.
 3. The die-cast component according to claim 1, wherein the temperable aluminum alloy has at least one of the group consisting of: from greater than 6.5 to 9.0 wt % silicon (Si), from 0.3 to 0.5 wt % magnesium (Mg), from 0.3 to 0.6 wt % manganese (Mn), from 0.15 to 0.3 wt % zinc (Zn), from 0.10 to 0.20 wt % copper (Cu), from 0.10 to 0.25 wt % iron (Fe), from 0.05 to 0.15 wt % titanium (Ti), and from 0.015 to 0.025 wt % strontium (Sr).
 4. The die-cast component according to claim 3, wherein the temperable aluminum alloy has at least one of the group consisting of: from greater than 6.5 to 8 wt % silicon (Si), from 0.15 to 0.25 wt % zinc (Zn), from 0.15 to 0.25 wt % iron (Fe).
 5. The die-cast component according to claim 1, wherein the temperable aluminum alloy has up to 0.05 wt % manganese (Mn) and/or up to 0.05 wt % copper (Cu).
 6. A body component for a motor vehicle with a die-cast component according to claim
 1. 7. The body component according to claim 6, with at least one punch rivet and with another component, wherein the die-cast component is firmly connected to the other component by the punch rivet.
 8. A motor vehicle with a body component according to claim
 6. 9. A method for producing a die-cast component according to claim 1, wherein the method comprises a heat treatment with the following steps in the indicated sequence: at least a two-stage annealing, comprising at least a first annealing at a temperature in a range from 320° C. to 450° C. for a duration of from 20 minutes to 75 minutes and a second annealing at a temperature in a range from 510° C. to 540° C. for a duration of from 5 minutes to 35 minutes, quenching with a temperature gradient in a range of greater than 4 K/s and at least a three-stage artificial aging, comprising at least a first artificial aging at a temperature in a range from 100° C. to 180° C. for a duration of from 40 minutes to 150 minutes, a second artificial aging at a temperature a the range from 180° C. to 300° C. for a duration of from 30 minutes to 100 minutes, and a third artificial aging at a temperature in a range from 230° C. to 300° C. for a duration of from 5 minutes to 120 minutes.
 10. The method according to claim 9, wherein the first annealing takes place at a temperature in a range from 390° C. to 410° C. and/or for a duration of from 50 minutes to 70 minutes.
 11. The method according to claim 9, wherein the second annealing takes place at a temperature in a range from 520° C. to 535° C. and/or for a duration of from 25 to 30 minutes.
 12. The method according to claim 11, wherein the second annealing takes place at a temperature in a range from 525° C. to 535° C.
 13. The method according to claim 9, wherein the quenching takes place with a temperature gradient in a range from 7 K/s to 20 K/s.
 14. The method according to claim 9, wherein the first artificial aging takes place at a temperature in a range from 140° C. to 160° C. and/or for a duration of from 110 minutes to 130 minutes.
 15. The method according to claim 9, wherein the second artificial aging takes place at a temperature in a range from 190° C. to 210° C. and/or for a duration of from 50 minutes to 70 minutes.
 16. The method according to claim 9, wherein the third artificial aging takes place at a temperature in a range from 230° C. to 270° C. and/or for a duration of from 10 minutes to 30 minutes. 